This protocol contains two components, each assigned a separate Duke IRB number. The first component utilizes 131Iodine-labeled Me1-14 F(ab')2 monoclonal antibody fragment in the treatment of patients with neoplasms metastatic to the leptomeninges. The purpose of this study is to determine the safety and maximum tolerated dose of intrathecal 131I-labeled Me1-14 F(ab')2 monoclonal antibody fragment in patients with neoplasms metastatic to the leptomeninges. The second component utilizes 131I-labeled Me1-14 F(ab')2 monoclonal antibody fragment in the treatment of patients with primary or metastatic malignant melanoma and other brain tumors with surgically created cystic resection cavities. The purpose of this study is to determine the safety and maximum tolerated dose of 131I-labeled Me1-14 F(ab')2 monoclonal antibody fragment administered into surgically created cystic tumor resection cavities in patients with primary or metastatic malignant melanoma and other brain tumors. Both disease entities are devastating, incurable neurologic complications of cancer where present treatments are inadequate. The development of monoclonal antibodies has provided the potential for more specific therapy of tumors which are reactive with the monoclonal antibody or antibody fragment. Antibodies that are specific to the tumor cells and that do not react with normal brain or spinal cord can be conjugated with therapeutic radioisotopes, such as 131I. This conjugate can then be delivered intrathecally for leptomentingeal neoplasms or into a surgically-created resection cavity for brain tumors to deliver a therapeutic dose of radiation with relative specificity for the tumor cells. Radiolabeled monoclonal antibodies may be a significant new therapeutic modality for these disease entities. These are the first studies in the United States to test such compartmental therapy of leptomeningeal neoplasms and brain tumor resection cavities with radiolabeled monoclonal antibodies.